Reclosable plastic containers made from a thermoplastic sheet having opposing rib and groove fastener elements (also called male and female interlocking closure profiles) are well known and described, for example, in U.S. Pat. Nos. 4,736,496; 4,741,789; 4,755,248; 4,764,977; 4,812,056; 5,009,828; 5,012,561; 5,022,530 and 5,070,548. One example of such a reclosable plastic container or bag is the Ziploc.RTM. brand food storage bag.
Typically, the male and female-type interlocking closure profiles are either manufactured separately-as strips and thereafter attached to a web of polymeric sheet as described in U.S. Pat. No. 3,462,332 or the closure profiles and sheet are extruded as an integral unit from a single die such as described in U.S. Pat. No. 3,340,116.
The industry is aware that width of the gap in the female or groove member of the closure profile is crucial to the proper functioning and accurate mating of the groove and rib or head members. Where the gap is too wide, for example, the closure profiles separate too easily providing a weak closure for plastic containers and resulting in leakage through the closure of the plastic container. Where the gap is too narrow, the closure profiles are difficult to mate together, both during manufacture of the plastic containers and later by the end user of the final product. There is, therefore, a need in the industry to properly, accurately and consistently control the gap width of the female profile.
Various methods have heretofore been used to control gap width of a female profile which, generally, include streams of gaseous or liquid coolant directed onto the surfaces of the closure profiles. For example, U.S. Pat. No. 5,106,566 issued to McCree discloses a process and apparatus for controlling the gap width of a female closure profile and fixing the configuration of the profile while simultaneously cooling the profile utilizing a flow of cooling fluid onto the closure profile.
While the method and apparatus disclosed in U.S. Pat. No. 5,106,566 is satisfactory, it is desired to provide an alternative process and apparatus for controlling gap width of a closure profile which could be used without the need for a liquid coolant for the specific purpose of maintaining the gap width because using a flow of liquid, alone, can still provide inconsistent gap widths depending on the control of such things as container stock production rates and conditions, the liquid coolant pressure, temperature and direction of application and force of a liquid coolant impinging upon the surfaces of the closure profiles.
It is, therefore, desired to provide a process and apparatus for accurately controlling the critical dimensions of a closure profile, during the manufacture of plastic container stock material at varying production rates, by mechanically maintaining the gap width of the closure profile.
It is also desired to provide a process and apparatus for mechanically altering a closure profile by a slight permanent deformation, resulting in a desired closure profile configuration having a desired predetermined fixed closure force.